I had a number of responses to my question asking how clubs manage log keeping and members wanting to fly;
Ian McPhee of Byron Bay responded that  his club used air-switches and Hobbs
Justin Couch of Southern Cross – We use our own system “Electronic Log” and update the Maintenance Releases monthly.  All entries are based on readings from the VDO timekeeping device.
Colin Gross shared a system used by Hunter Valley. Our Club has a complete gliding system that we use to log flights and administer the club. Among many other features it has an "Intentions" function There is a complete "demo" version that is available to all.
The complete system could be made available to any club - contact me This email address is being protected from spambots. You need JavaScript enabled to view it.
Alex Husy from Kingaroy shared a system he uses in Berne Switzerland which is based on an open calendar.  The calendar allows members to put in their intentions regarding flying on a specific date and airplane, but it is not a reservation itself.
We also put the roster in the calendar, so everyone can see who will be present. Tuggies and Instructors can manage replacements and make direct modifications to the roster.